JP3140283B2 - Audio equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device, and more particularly, to an improvement in an S / N ratio of an audio device having a so-called tone control function and a fader control function.

[0002]

2. Description of the Related Art FIGS. 4 and 5 show a reproducing circuit for one channel (R) of a cassette tape player as an example of a conventional audio apparatus. The apparatus shown in FIG. 4 has a so-called tone control function (sound quality adjustment function) in addition to a so-called volume control function (volume adjustment function).
Having. 5 has a so-called fader control function in addition to a so-called volume control function. In any case, not only the whole volume adjustment of the audio signal but also another volume adjustment of the adjusted audio signal is performed.

In FIG. 4, 10 is a read head, 11 is a preamplifier, 12 is an electronic volume for volume control, 13 is a control signal generating circuit for generating a volume control signal E, and 14 is a specific frequency band for tone control. A corresponding band-pass filter (BPF) or a low-pass filter (LPF) for raising a low frequency band, a high-pass filter (HPF) for raising a high frequency band, 15 is an electronic volume for tone control, and 16 is a control for generating a tone control signal F. A signal generating circuit, 17 is a so-called mute circuit, 18 is a synthesizing circuit, and 19 is a power amplifier for driving a speaker.

[0004] The volume VR1 indicates whether the volume should be reduced according to whether the set position is below or above. Therefore,
Control signal generating circuit 1 to which the setting of volume VR1 is input
3 generates a control signal E having a current value corresponding to the setting of the volume VR1 and outputs it to the electronic volume 12 as the control signal. The electronic volume 12 performs a volume control function by changing an attenuation rate for an audio signal according to the control signal E.

The volume VR2 indicates whether the filter 14 should emphasize a specific frequency band in accordance with whether the set position is below or above. Therefore, the control signal generating circuit 16 which has input the setting of the volume VR2,
A control signal F having a current value corresponding to the setting of 2 is generated and output to the electronic volume 15 as the control signal. Here, the electronic volume 15 includes a voltage / current conversion circuit, a current ratio distribution circuit receiving an output of the voltage / current conversion circuit, and a current / voltage generating an output after volume control upon receiving an output of the current ratio distribution circuit. Conversion circuit, to control the operating current of the voltage / current conversion circuit to an operating current corresponding to the allowable input to secure a dynamic range, and to simultaneously control the operating current of the current ratio distribution circuit to obtain a total. The volume is adjusted. The control signal in this case is F, and performs a tone control function by changing the attenuation rate for the audio signal in accordance with the control signal F.

The reproducing circuit having such a configuration operates as follows. An audio signal is read from a tape (not shown) via the read head 10, and this is initially amplified by a preamplifier to generate an audio signal A. By this amplification, the signal level of the audio signal A is made to substantially fill the dynamic range in the signal processing circuit. Then, the volume of the audio signal A is controlled by the electronic volume 12 to be an audio signal B having a desired signal level.

Further, the audio signal B is filtered by the filter 14.
And an electronic signal 15 having only a specific frequency band component through the electronic volume 15,
8, a tone-controlled audio signal is generated in addition to the audio signal B. This is output from the speaker as final sound by the power amplifier 19 to the outside of the apparatus.

Here, the mute circuit 17 is specifically a switch circuit composed of a transistor, and is turned off only when the tone control signal F indicates that the output of the electronic volume 15 is to be cut off. Turn on. Thus, when the output of the audio signal is reduced by tone control or the like, noise generated by a circuit for tone control or the like, particularly, the electronic volume 15 is cut.

The apparatus of FIG. 5 does not have the filter 14 and the synthesizing circuit 18 which are present in the apparatus of FIG. 4, and has another set of electronic volume, mute circuit, power amplifier and speaker (R) which are not present in the apparatus of FIG. −Rear) is different from the apparatus of FIG. The electronic volume 15 attenuates the audio signal B not for tone control but for fader control. Considering the system from the read head 10 to the speaker (R-Front) via the electronic volume 15, it is almost the same as the previously described tone control system. Therefore, although a detailed description of this device is omitted, fader control is possible in short, and the mute circuit 17 is also turned off only when the fader control signal F indicates that the output of the electronic volume 15 is to be reduced. At that time, the noise caused by the electronic volume 15 is cut.

[0010]

In such a conventional audio device, an electronic volume is employed from the viewpoint of measures against noise and easiness of control by routing wiring from a volume that is directly operated, and an entire audio signal is used. The electronic volume is used not only for adjusting the volume of the audio signal but also for other volume adjustment such as partial adjustment of an audio signal. Such an electronic volume is a so-called VCA
Among them, a type in which the operating current is not affected by the control signal is adopted because of its good temperature characteristics.

However, this type of electronic volume has the property that the output noise level does not become zero even when the output signal level is reduced. For this reason, as described above, conventionally, a mute circuit is arranged on the output side of the electronic volume to take a measure, but the mute circuit works only in a limited case and is not effective during normal operation of the electronic volume. . In particular, when tone control such as slight emphasis is performed, noise is relatively noticeable since the noise level is always the same while the emphasis component of the audio signal is small. Under a configuration in which another volume adjustment is performed after adjusting the volume of the entire audio signal, since this noise is output as it is, there is a problem that the S / N ratio does not become very good.

On the other hand, by changing the order of the volume adjustment and finally performing the overall volume adjustment including the noise, S
Although it is conceivable to improve the / N ratio, this configuration has another problem that the dynamic range is exceeded by adding an emphasis component or the like to an audio signal having a full dynamic range, and this problem is prevented from occurring. For this reason, a complicated circuit configuration is forced or the S / N ratio is deteriorated, so that this configuration is difficult to adopt.

In particular, when the electronic volume having the above configuration is used for volume control of a derived signal derived from the audio signal, such as an output of an equalizer or a fader circuit that receives the audio signal,
When the volume of the derived signal is reduced, the ratio between the current of the input audio signal and the operating current of the voltage / current conversion circuit of the electronic volume becomes unbalanced, and the dynamic range cannot be secured or noise cannot be reduced. There is such a problem. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to realize an audio device having a good S / N ratio.

[0014]

SUMMARY OF THE INVENTION To achieve this object, an audio apparatus according to the present invention has an audio signal according to a first control signal indicating an overall first volume adjustment level. The first volume adjustment is performed, and an output of an equalizer or a fader circuit that receives the audio signal is output in response to a second control signal indicating an adjustment level of a second volume adjustment for a derived signal derived from the audio signal. In the audio apparatus for performing the second volume adjustment after the first volume adjustment, a voltage / current conversion unit, a current ratio distribution unit receiving an output of the voltage / current conversion unit, and an output of the current ratio distribution unit. And a current / voltage converter for receiving the second volume adjustment and generating the output after the second volume adjustment. The voltage / current converter receives the derived signal after the first volume adjustment and operates the current / voltage converter. Wherein it is controlled in accordance with the first control signal a second operating current of the current ratio distribution unit by the control signal is intended to be controlled.

[0015]

As described above, the control of the operation current of the voltage / current conversion unit of the electronic volume for adjusting the volume of the derived signal derived from the audio signal, such as the output of the equalizer and fader circuit receiving the audio signal, is performed by the audio signal. Since the control is performed in accordance with the control signal for performing the overall volume adjustment, the operating current of the voltage / current converter increases when the level of the input audio signal is high, and when the level is low, the operation current of the voltage / current converter increases. The operating current becomes smaller,
The level of the audio signal input to the electronic volume and the level of the operating current of the voltage / current conversion unit change according to the magnitude, and the ratio of these is controlled to a state close to a relatively constant value. In addition, since the operating current of the voltage / current conversion unit is not controlled to an operating current that is more than necessary, generation of noise can be suppressed. As a result, a dynamic range can be secured and noise can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the audio apparatus according to the present invention will be described below with reference to the drawings. 1 and 2 show a reproduction circuit for one channel (R) of a cassette tape player as an embodiment. The apparatus shown in FIG. 1 exhibits a tone control function in addition to the volume control function, and corresponds to the apparatus shown in FIG. On the other hand, the device shown in FIG. 2 exhibits a fader control function in addition to the volume control function.
It corresponds to the thing. 1 and 2 show the same components as those in FIGS. 4 and 5 with the same reference numerals. Therefore, these descriptions will be omitted, and the description will focus on a new electronic volume 25 provided in place of the conventional electronic volume 15.

The electronic volume 25 in FIG. 1 includes a voltage / current converter 25a, a current ratio distributor (not shown) receiving the output of the voltage / current converter 25a, and a current ratio distributor (see FIG. 1). (Not shown) and a current / voltage converter (not shown) for generating an output after volume adjustment. Here, the voltage / current converter 25a controls the current of the current source 25b to change the operating current. This operating current is controlled by a control signal E which controls the volume of the overall audio signal.

The electronic volume 25 receives the audio signal C
Is a signal input, a tone control signal F is a control input, and an audio signal D is an electronic volume. The audio signal is obtained by changing a current distribution ratio (current ratio) of a current ratio distribution unit according to the tone control signal F. An audio signal D whose volume is controlled is generated from C. This point is the same as the conventional electronic volume 15, but differs in that the operating current of the voltage / current converter 25a changes according to the level of the input audio signal.

That is, the present embodiment differs from the conventional electronic volume control 15 in that the volume control signal E is also used as a control input, and the operating current is improved so as to change according to the volume control signal E. FIG. 3A shows a specific circuit example of the electronic volume 25 in order to explain this point in detail. this is,
This is a circuit in which the current ratio distribution unit 26 is stacked on the voltage / current conversion unit 25a, and the current / voltage conversion unit 27 includes a resistor R
1 is in charge. FIG. 3B shows a specific circuit example of the control signal generation circuit 16 using a differential circuit. The control signal generation circuit 13 uses a current mirror to apply a voltage signal from a variable resistor that is manually controlled in volume. It is generated as a tone control signal F or a volume control signal E and sent to the electronic volume 25.

The voltage / current converter 25a is generally a differential circuit. The audio signal input C is converted into a pair of differential currents by a differential transistor pair Q1 and Q2, and is then converted into a voltage signal by a resistor R1. Return to generate a signal output D. This differential current component is included in the respective collector currents of the transistor pair Q1 and Q2. In this collector current, the ratio of the current fluctuating due to the operation of the differential transistor pair Q1 and Q2 to the remaining non-variable current is: It is controlled according to the tone control signal F. Thus, the operating current I is not influenced by the tone control signal F, and the temperature characteristics are ensured. That is, assuming that the control signal F (the amount of tone control current) is a, (1−a), the value of the current I ₁ supplied from the current mirror on the left side of the drawing to the collector of the transistor is a × (I + i) / 2 and the current I ₂ flowing through the collector of the centrally connected transistor
Is (I + i) × (1-a) / 2 + (I−i) ×
(1−a) / 2 = I × (1−a). The value of the current I ₃ which is supplied from the right side of the current mirror to the collector of the transistor becomes a × (I-i) / 2. Therefore, the output audio signal D is controlled only by the control amount a of the tone control current F, thereby compensating the temperature characteristics.

The current obtained by extracting only the difference between the pair of differential currents of the control signal E and inverting the difference by the current mirror is the operating current I of the electronic volume 25, more specifically, the differential transistor pair of the electronic volume 25. The operating current I of Q1 and Q2 is used. Thereby, the operating current I is variably controlled according to the volume control signal E. The conventional electronic volume 15 has a constant operating current I. Generally, the dynamic range and the generated noise level are determined in accordance with the magnitude of the operating current I of the differential transistor pair Q1, Q2. .

The operation of the reproducing circuit of FIG. 1 in which the electronic volume 25 having such a configuration is used as an electronic volume for tone control will be described. An audio signal A having a full dynamic range from a tape (not shown), an audio signal B whose volume has been controlled to a desired level,
The audio signal C composed of the specific frequency band component is
Generated in the same manner as in the past. Electronic volume 2
5, the audio signal C is attenuated in accordance with the tone control signal F to obtain an audio signal D, which is added to the audio signal B by the synthesizing circuit 18 to generate a tone-controlled audio signal. The final sound is output from the speaker to the outside of the device. This is also the same as in the past.

Therefore, the conventional functions are ensured for the volume control function and the tone control function. Here, paying attention to the noise generated in the electronic volume 25, this noise level changes in proportion to the volume control signal E unlike the related art. That is, when the final sound output is high, the noise level is the same as the conventional one, but when the final sound output is low, the noise level is low unlike the conventional one. Therefore, only when the final sound output is large, the same S
/ N ratio, but at other times the S / N ratio is improved. Further, a mute circuit is not required.

The device shown in FIG. 2 has the same configuration as the conventional device except that an electronic volume 25 is adopted as an electronic volume for fader control, and an operation current of the electronic volume 25 is controlled according to a volume control signal E. . Therefore, although the description is omitted, even in this device, the functions of the volume control function and the fader control function are the same as the conventional functions, and the electronic volume 25
Are suppressed and the S / N ratio is improved.

[0025]

As can be understood from the above description, in the audio apparatus of the present invention, the volume of a derived signal derived from the audio signal, such as the output of an equalizer or fader circuit receiving the audio signal, is adjusted. The control of the operating current of the voltage / current converter of the electronic volume is controlled according to the control signal for adjusting the overall volume of the audio signal. The operating current increases, and when the operating current decreases, the operating current of the voltage / current converter decreases. The level of the audio signal input to the electronic volume and the level of the operating current of the voltage / current converter change correspondingly. These ratios are controlled to be relatively close to a constant value. In addition, since the operating current of the voltage / current conversion unit is not controlled to an operating current that is more than necessary, generation of noise can be suppressed. As a result, a dynamic range can be secured and noise can be reduced.

[Brief description of the drawings]

FIG. 1 is a reproduction circuit for one channel having a tone control function in a cassette player as an embodiment of an audio apparatus having the configuration of the present invention.

FIG. 2 is a reproduction circuit for one channel having a fader control function in a cassette player as another embodiment of the audio apparatus having the configuration of the present invention.

FIG. 3 is a detail of some of those circuits.

FIG. 4 is a reproduction circuit for one channel of a conventional cassette player with a tone control function.

FIG. 5 is a reproduction circuit for one channel of a conventional cassette player with a fader control function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Read head 11 Preamplifier 12 Electronic volume 13 Control signal generation circuit 14 Band-pass filter (BPF) 15 Electronic volume 16 Control signal generation circuit 17 Mute circuit 18 Synthesis circuit 19 Power amplifier 25 Electronic volume

Claims (1)

(57) [Claims] 1. An equalizer and a fader circuit for an equalizer and a fader circuit that perform the first volume adjustment on an audio signal according to a first control signal indicating an overall first volume adjustment level. An audio device that performs the second volume adjustment after the first volume adjustment in accordance with a second control signal indicating an adjustment level of a second volume adjustment for a derived signal derived from the audio signal, such as an output. A voltage / current conversion unit, a current ratio distribution unit receiving the output of the voltage / current conversion unit, and a current / voltage conversion unit receiving the output of the current ratio distribution unit and generating the output after the second volume adjustment. The voltage / current converter receives the derived signal after the first volume adjustment, and its operating current is controlled according to a first control signal, and the current ratio distribution unit is controlled by the second control signal. Movement Audio and wherein the current is controlled.